The P.I. and collaborator's laboratories were the first to identify novel cytoplasmic foci known as GW bodies (GWBs), which are now known to be enriched with human autoantigens important in the effector arm of the RNA interference (RNAi) pathway. The initial characterization was achieved via expression cloning using a human autoimmune serum containing antibody to GW182, an 182KD protein autoantigen with unique glycine-tryptophan (GW) repeats that is specifically localized to GWBs. GW182 was shown to be associated with selected messenger RNAs (mRNAs) and the protein Ago2 which is the key enzyme in the RNAi mediated processing of mRNA. Our recent data showed that short interference RNAs (siRNAs) and microRNAs (miRNAs) are localized to GWBs and effective RNAi function requires intact GWBs. Taken together, the working hypothesis is that GWBs are novel sites regulating cytoplasmic mRNA levels via the siRNA/miRNA dependent RNAi process by maintaining stability and/or controlling degradation of mRNA. To date, human autoantibodies to GWBs are known to have overlapping subsets that recognize GW182, Ago2, and other autoantigens being characterized in the P.l.'s lab. Three Specific Aims have been designed to help further characterize the biological significance of GWBs in normal and in systemic rheumatic diseases including systemic lupus erythematosus (SLE) and Sjogren's syndrome (SjS) based on the preliminary data linking anti-GW182 autoantibody to these 2 autoimmune diseases. The interest in SjS is further developed with the observed overexpression of GW182 in certain foci of SjS minor salivary gland biopsies and the co- expression of anti-52kD SSA/Ro autoantibody in anti-GW182 positive autoimmune sera. The goal of the proposed study is to explore the biological functions of these novel subcellular foci which may shed some insight as to their involvement in the pathogenesis of SLE and SjS. Specific Aim 1 will address the biology of GW182, Ago2 and other closely associated autoantigens detected in GWBs. Specific Aim 2 will characterize anti-GWB antibodies in established mouse models of autoimmune diseases and test the hypothesis that autoimmune responses to GWBs are related to deregulation of GWB expression in target organs possibly resulting in defects in RNAi. Specific Aim 3 will characterize the significance of anti-GWB antibodies in human diseases and follow up on the preliminary data that GW182 and SS-B/La, a known major autoantigen in SjS and SLE, were overexpressed in foci of SjS salivary gland biopsies. The proposed studies will help define the biological role of GWBs in the pathogenesis of SLE and SjS. The animal models will provide the means to test hypotheses that are relevant to the induction of these autoantibodies targeting GWBs. Implication for mi RNA in cancer has been described recently and this proposed study will address whether there may be a role for miRNA deregulation in autoimmune diseases.